Air cycle machines are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the initial ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the air cycle machine before the air is delivered to the aircraft cabin.
Air cycle machines typically include rotating parts connected to a rotating shaft that extends through static parts of the air cycle machine. Each end of the rotating shaft is supported with a journal bearing to mount the rotating shaft in the static parts of the air cycle machine. The journal bearings are supported by journal bearing support sleeves as part of a compressor housing. During assembly of the air cycle machine, the static parts need to be closely aligned with one another so that the journal bearings on either end of the air cycle machine can also be closely aligned. It is important to closely align the journal bearings so the rotating shaft rotates about an axis through the center of the rotating shaft. Any misalignment between the journal bearings can cause rubbing and wear between the rotating parts and the static parts. Motor failure, misalignment, or bearing failure can result in damage to the journal bearing support sleeve of the compressor housing. Replacing the compressor housing can be expensive.